1. Field of the Invention
The present invention relates to an apparatus and method for driving a display device and, more particularly, to an apparatus and method for driving a liquid crystal display device which improves the brightness of the liquid crystal display device.
2. Discussion of the Related Art
In general, a cathode ray tube (CRT), one of display devices that is being widely used, is mainly used for a monitor for TVs, measuring instruments, information terminals or the like. However, due to its size and weight, the CRT is not widely used for small and light electronic products. Accordingly, in order to replace the CRT, a liquid crystal display (LCD) device has been developed, which has such advantages as small size, lightweight and low-power consumption. Because of these advantages, the demand for the LCD device is continuously increasing.
The LCD device takes advantage of the principles of refractive anisotropy and polarization. By controlling the alignment direction of the liquid crystal molecules, an amount of light passing through the LCD device can be adjusted due to the refractive anisotropy of the liquid crystal molecules. Of various types of LCD devices, an active matrix LCD device is currently most widely used due to its superior picture quality, in which a thin film transistor and a pixel electrode connected to the thin film transistor are arranged in a matrix configuration.
The active matrix LCD device includes a display panel in which a plurality of pixels are arranged in a matrix configuration and a driving part for driving the pixels. The display panel includes a thin film transistor array(TFT) substrate and a color filter(CF) substrate which face each other and are attached to each other with a uniform cell-gap. A liquid crystal layer is provided between the CF substrate and the TFT substrate. A common electrode and a pixel electrode are formed in the display panel and apply an electric field to the liquid crystal layer. Accordingly, when a voltage is applied between the common and pixel electrodes, the liquid crystal molecules of the liquid crystal layer rotates according to the electric field due to the dielectric anisotropy, thereby displaying texts or images.
FIG. 1 is a plan view illustrating a pixel structure of a liquid crystal display device according to a related art.
Referring to FIG. 1, the LCD device includes a plurality of pixels 120 arranged in a matrix configuration on a substrate 110, and each pixel 120 has red, green and blue (R, G and B) sub-pixels. The LCD device having such a construction is not a self-emitting device, so that a back-light is provided at the rear of the substrate 110 to generate white light. The white light generated from the back-light passes through the R, G and B sub-pixels, thereby displaying images. When the white light generated from the back-light passes through the R, G and B sub-pixels, each of the R, G and B sub-pixels transmits an amout of light in a corresponding range of wavelength (wavelength ranges of red, green and blue lights) and absorbs light in other ranges of wavelength. Therefore, the LCD device has a disadvantage in that it has a lower brightness, compared with the CRT. Accordingly, a LCD device having four sub-pixels in one pixel has been recently proposed in order to improve the brightness of the LCD device.
FIG. 2 is a plan view illustrating a pixel structure of a LCD device according to a related art in which one pixel has four sub-pixels. With reference to FIG. 2, the LCD device includes a plurality of pixels 220 arranged in a matrix configuration on a substrate 210. Each pixel further includes red, green, blue and white (R, G, B and W) sub-pixels. The LCD device having the R, G, B and W sub-pixels in one pixel 220 has a higher brightness than the LCD device having the R, G and B sub-pixels in one pixel 120 shown in FIG. 1. This will be described in detail.
When white light generated from a back-light passes through the R, G and B sub-pixels, each of the R, G and B sub-pixels transmits an amount of light in a corresponding range of wavelength (wavelength ranges of red, green and blue lights) and absorbs light in other ranges of wavelength. By controlling the amounts of the transmitted red, green and blue lights, the LCD device determines a color displayed at the pixel 220. At this time, the white W sub-pixel controls the amount of the white light generated from the back-light in accordance with the amounts of the transmitted red, green and blue lights. That is to say, the W sub-pixel improves the brightness of the LCD device by increasing the brightness of the white light in the red, green and blue lights transmitted from the red, green and blue (R, G and B) sub-pixels.
However, when displaying a monochromatic light (red light, green light or blue light) or a mixture of two lights out of red light, green light and blue light at the pixel 220, the LCD device has a lower brightness than the LCD device in which one pixel 120 has the R, G and B sub-pixels. In other words, when displaying a monochromatic light or a mixture of two lights out of the red light, the green light and the blue light at the pixel 220, the transmitted light does not include white light, and thus the W sub-pixel blocks the white light generated from the back-light according to the image information. In addition, assuming that the LCD device of FIG. 1 has the same size and resolution as the LCD device of FIG. 2, a size of each sub-pixel of FIG. 2 (R, G, B and W sub-pixels) is smaller than that of each sub-pixel of FIG. 1 (R, G and B sub-pixels).
As a result, when displaying a monochromatic light or a mixture of two lights at the pixels 220, the W sub-pixel does not transmit white light, and the LCD device having the R, G, B and W sub-pixels in one pixel 220 has a lower aperture ratio than the LCD device having the R, G and B sub-pixels in one pixel. Accordingly, the LCD device haivng the R, G, B and W sub-pixels in one pixel 220 has a lower brightness than the LCD device having the R, G and B sub-pixels in one pixel.